Generally, a device for driving a motor refers to a device capable of controlling a speed of the motor with a high efficiency by supplying power supplied from an external power source to the motor via varying a voltage and frequency thereof.
FIG. 1 is a perspective view of a conventional device for driving a motor. FIG. 2 shows a state in which an input/output (IO) cover is removed in FIG. 1.
Referring to FIGS. 1 and 2, a conventional device 1 for driving a motor may be constructed such that a heat sink 12 is disposed under a middle base 11 so as to be exposed, and a circuit module not shown is disposed above the middle base 11, and a main housing 13 accommodates the circuit module.
In this connection, above the main housing 13, an IO cover 14 for opening and closing the 10 circuit module may be disposed.
Further, an auxiliary housing 15 may be disposed on one side face of the main housing 13 adjacent to the IO cover 14. Wires or the like from an outside may be accommodated in the auxiliary housing 15.
The auxiliary housing 15 may be fastened to a top of the heat sink 12 via a first screw coupling 15a. The IO cover 14 may be fastened to a fastening bracket 16 disposed on one side face of the auxiliary housing 15 via a second screw coupling 16a. 
The conventional device 1 for driving a motor having such a structure may have following problems.
First, the auxiliary housing 15 must be fastened to a metal part such as the heat sink 12. Thus, a separate structure defining the fastening structure made of the metal material is required. Thus, there is a problem that a product cost increases and an assembling time increases.
Second, since the heat sink 12 should not be miniaturized for coupling the auxiliary housing 15 thereto as described above, miniaturization and lightening of an overall product may not be achieved.
Thirdly, the auxiliary housing 15 is fixed to the device 1 for driving the motor while is coupled via the first screw-coupling 15a only to the heat sink 12. Such a structure may be vulnerable to a load of the wiring or other objects accommodated in the auxiliary housing 15. That is, although the auxiliary housing 15 is comparatively robust relative to a vertical load, the auxiliary housing 15 is vulnerable to a horizontal load, particularly, to a shearing stress, thereby being damaged.